Field olfactometers are used to assess environmental odors, for example, odors from agricultural or industrial operations. Under some regulatory schemes, odors which may emanate from a commercial operation must be controlled to a certain level. An odor level is commonly defined for regulatory purposes by a volumetric dilution ratio of odor-free air to sample air containing the odor-causing chemical or chemicals. In particular, the dilution ratio at which the odor is first detectable by a normal human olfactory system is defined as the dilution to threshold (“D/T”) for the odor. A regulatory scheme may require that an odor from a given commercial operation must remain below a certain D/T at a given distance from the operation. For example, the Missouri Air Pollution Control Program Laws and Regulations have historically set the maximum D/T for an odor at a value of 7:1 for emissions from confined animal feeding operations. Also, D/T values below the maximum D/T may be defined as having some other significance in a regulatory scheme. For example, Missouri DNR has also utilized a D/T limit value of 5.4:1 from field screening as an early warning to trigger more extensive laboratory testing.
There are two options for measuring the D/T for an odor that may be emanating from a commercial operation. A first option is to collect sample air at various locations around the operation and then take the collected sample air to a laboratory for analysis using some laboratory-based olfactometry method. However, laboratory-based olfactometry is expensive and thus impractical for many applications. The second option for measuring the D/T for an environmental odor is referred to as field olfactometry. Field olfactometry is performed using a portable field olfactometer which a user may operate to measure the D/T for a given odor at various locations around a commercial operation from which the odor emanates.
Prior field olfactometers include a device known as the Barneby-Sutcliffe Box Scentometer (the “Box Scentometer”) which was developed in the 1950s. The Box Scentometer includes a diluent air path having an activated carbon filter, a sample air path, a series of restrictions which may be selected for the sample air path, and two inhalation tubes configured to align with a user's nostrils. In operation, a user places their nostrils against the two inhalation tubes and inhales in order to draw air through the two flow paths. The diluent air path takes ambient air through the activated carbon filter to remove odors. The user first blocks the sample air path and draws air only through the diluent air path to ensure that the device is initially filled with only the filtered, odor-free air. After this initialization, the filtered, odor-free air is used as diluent for the sample air which is then allowed to flow through the sample air path in response to the user's inhalation. Each restriction for the sample air path is an orifice sized to produce a discrete dilution ratio when the user inhales against the inhalation tubes with sufficient force. By operating the Box Scentometer using first the smallest restriction for the sample air path, and then sequentially each larger flow restriction until the odor is detected, the user can identify the D/T for the odor.
The device sold under the trademark Nasal Ranger® is another prior art field olfactometer. The Nasal Ranger olfactometer is fundamentally very similar to the Box Scentometer in that it includes a first flow path for providing filtered, odor-free diluent air, a second path for sample air, and a series of restrictions which may be selected to restrict flow through the sample air path. Rather than the two inhalation tubes employed by the Box Scentometer, the nasal Ranger olfactometer includes a nose mask at an outlet end of the device. The mask provides a seal around the user's nose and allows the user to inhale through their nostrils into the device to draw diluent air and sample air through the device. In the Nasal Ranger olfactometer, the different sample air restrictions are mounted on a dial which the user may rotate so as to align the desired restriction with the sample air path through the device. The Nasal Ranger olfactometer also includes a flow meter which allows the user to see the flow rate through a mixing tube of the device to ensure that the flow rate is at a sufficient level to produce the dilution ratio intended for a given restriction.
As with the Box Scentometer, the user operates the Nasal Ranger olfactometer by first initializing the device with only filtered, odor-free air, and then sequentially using the different sample air restrictions beginning with the smallest flow restriction. The smallest restriction for the sample air path produces the highest dilution ratio in response to a nasal inhalation at a proper rate into the mask of the device. If the odor under assessment is detected when the user inhales at the desired rate with the smallest flow restriction aligned with the sample air path, then the user may record that the D/T of the odor is at least at the dilution ratio produced by operation using the smallest restriction. However, if the odor under assessment is not detected at the dilution ratio produced by the smallest flow restriction in response to a nasal inhalation into the olfactometer at the desired rate, the user rotates the dial to align the next larger restriction with the sample air path and performs another inhalation. The user repeats this operation using sequentially larger flow restrictions until the odor is detected. At the operation at which the odor is detected, the user may record that the odor under assessment is present in the atmosphere at that location and time at a D/T corresponding to the dilution ratio produced using the flow restriction in place for that operation of the olfactometer.
Another prior art field olfactometer is known as the Mask Scentometer. The Mask Scentometer includes a one-quarter face respirator mask with two input cartridges defining two input flow paths. One cartridge is fitted with an activated carbon filter to provide filtered, odor-free air to the mask to serve as a diluent. The other cartridge includes a dial mechanism similar to that employed by the Nasal Ranger olfactometer with a series of different sized orifices. The user may operate the dial to align any one of the different orifices so as to allow sample air to be drawn in to the device through the selected orifice in response to a user's nasal inhalation into the mask. Each orifice which may be selected in the Mask Scentometer correlates to a particular dilution ratio between diluent air provided through the filter cartridge and sample air provided through the second cartridge given a desired total flow rate, that is, a desired user nasal inhalation rate, into the mask.
Aside from the fact that the Mask Scentometer is worn rather than simply manually held against the user's face to provide a seal around the user's nose, the operation of the device is very similar to the operation of the Box Scentometer and Nasal Ranger olfactometer. Once the user ensures that the mask is tilled with odor-free air by blocking the sample air path completely and inhaling filtered, diluent air into the mask, the user moves the dial to align the smallest restriction with the sample air path in the sample air cartridge. The user then inhales through their nostrils into the mask to draw diluent air through the first cartridge and sample air through the second cartridge. If the user detects the odor under assessment with that inhalation, then the user may record that the D/T for the odor is at least at the dilution ratio corresponding to the first, smallest flow restriction and the desired inhalation rate. If the user does not detect the odor with the first inhalation using the first and smallest flow restriction, the user rotates the dial to align the next largest orifice/flow restriction and inhales again. The user continues this process using sequentially larger flow restrictions until the odor is detected. The user may then record that the D/T for the odor under assessment is at the dilution ratio corresponding to the flow restriction in use when the odor is first detected.
There are a number of problems encountered with the prior art field olfactometers. First, the prior art field olfactometers are relatively expensive and thus the devices cannot be widely distributed to allow assessment of odors over large geographical areas and over extended periods of time encompassing a range of environmental conditions. This is a very serious drawback because odor plumes tend to be transient in nature and are variable with weather conditions. Also, with the Box Scentometer and Mask Scentometer, it is difficult to ensure that the nasal inhalation by the user is sufficient to produce the desired flow rate through the two flow paths of the device to result in the intended dilution ratio between diluent air and sample air. Even with the Nasal Ranger olfactometer, which incorporates a flow meter, it is difficult for the user to coordinate their observation of the meter with their operation of the device to ensure that the flow rate through the device is at a level to produce the desired dilution ratio.